EMC control can be applied at three levels, primary, secondary and tertiary.

Control at the primary level involves circuit design measures such as decoupling, balanced configurations, bandwidth and speed limitation, and also board layout and grounding. For some low-performance circuits, and especially those which have no connecting cables, such measures may be sufficient in themselves.

Digital circuit design

Analogue circuit design

Power switching circuit design

Motors and switches

PCB Layout

AC supply harmonics

At the secondary level the interface between the internal circuitry and external cables is invariably a major route for interference in both directions, and for some products (particularly where the circuit design has been frozen) all the control may have to be applied by filtering at these interfaces. Choice and mounting of cables and their connectors forms an important part of this exercise.

Power interface filtering

Signal interface filtering

Balanced interfaces

Isolated interfaces

Transient protection

Unshielded cables

Cable shielding

Cable ferrites

Cable routing and segregation

Cable connectors

Full shielding (the tertiary level) is an expensive choice to make and should only be chosen when all other measures have been applied. But since it is difficult to predict the effectiveness of primary measures in advance, it is wise to allow for the possibility of being forced to shield the enclosure.

In all cases, the flow of current in conducting structures - which can, loosely, be termed "grounding" structures such as chassis components - turn out to have a vital influence on how successful these measures are.

Enclosure shielding

Heatsinks and EMC

Grounding and bonding